Reversal by Mercaptoethanol of Protective Effect of Solutes Against Frost Injury of Red Cabbage

In confirmation of Maximov's earlier results, non-penetrating (sucrose) and penetrating (dimethylsulfoxide) substances lowered the frost killing temperature from -6°C in the control to -11° to -24°C, depending on the concentration. In contrast to his results, neither glycerol nor CaCl₂ provided as good or as consistent protection. The addition of 0.05 M mercaptoethanol overcame this protective effect either completely (low concentrations of protectant) or partially (high concentrations). The effect of the mercaptoethanol occurs during freezing and not during thawing. Since ethanol, without the mercapto-(SH) group, does not counteract the protective effect, such protection must be related in some way to the sulfhydryl group — perhaps by an effect on the disulfide and sulfhydryl groups of the proteins.     

Causes of vertical stratification in the density of Cameraria hamadryadella

1. The density of Cameraria hamadryadella, a leaf-mining moth, is vertically stratified within the crown of oak trees. It occurs at higher densities on foliage in the lower crown. 2. Oviposition preference tests indicate that females display no preference to oviposit on foliage from the lower tree crown over foliage from the upper tree crown. 3. Experiments in which potted trees were placed at various heights indicate that foliage nearest ground level receives more oviposition, and that the higher rates of oviposition on foliage near the ground is not caused by differences in quality between foliage from low or high in the tree crown. 4. Host-plant- and natural-enemy-mediated juvenile mortality and the abundance of parasitoids did not differ between the upper and lower crown. 5. Vertical differences in the timing of leaf production within the tree crown are unlikely to account for the observed gradient in the abundance of C. hamadryadella. Furthermore, the mean date of leaf fall does not differ among heights within the tree crown. 6. It is argued that microclimatic gradients and interspecific competition are also unlikely to account for the observed gradients in the density of C. hamadryadella within the tree crown. 7. Because of the absence of effects of other potentially causal factors, the most likely explanation for the gradient in density of C. hamadryadella is a lack of movement by females into the upper tree crown from overwintering, emergence, or resting sites located in the lower tree crown, combined with egg depletion by females as they move from the lower to the upper tree crown. 8. It is suggested that the lack of movement and egg depletion hypothesis should serve as the null hypothesis in studies of vertical stratification of tree-feeding insects. In the absence of evidence of an effect of foliage quality, natural enemies, plant phenology, interspecific competition, or microclimate, the movement and egg depletion hypothesis is the most reasonable.     

Amino-acid Sequence of Extracellular Ribonuclease (Barnase) of <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis>

THE ribonuclease, barnase, produced by Bacillus amyloliquefaciens has a molecular weight of 12,382, consisting of 110 amino-acid residues. It is one of the smallest proteins containing neither disulphide bonds nor non-peptide cross-Bnks which nevertheless maintain a well defined tertiary structure^1,2. The next smallest reported enzyme of similar nature is the lysozyme of phage T4, with 160 residues. The barnase structure is reversibly destroyed by denaturing solvents or heat², in what approximates a one step, highly cooperative, transition. Studies of this reaction should be very useful in illustration approaching the general problem of sequence-determined folding in proteins. In particular, thermodynamically meaningful quantitative differences in the stability of various genetic variants and chemically modified, or synthetic, barnases could be measured. Some work has been reported on the effect of various environmental parameters on the transition³ as well as the effects of modification by carboxypeptidases⁴. Full utilization of such data requires knowledge of both amino-acid sequence and three dimensional structurs. The complete amino-acid sequence is reported here (Fig. 1). The sequence was obtained by conventional procedures involving analysis of peptides isolated after hydrolysis of the native or modified protein by various proteases.

Open image in new window

     

Human Serum Cholinesterase,a Tetramer

AFTER electrophoresis of human serum in starch gel¹, there are at least four bands of Cholinesterase activity. Most of the enzyme is concentrated in the band with least mobility (C₄) while three faster moving bands (C₁, C₂, C₃) are of lower molecular weight as shown by gel filtration². Although electrophoresis in Polyacrylamide reveals additional bands³, all seem to be a single genetic entity as shown by experiments on persons homozygous for the silent gene^4,5. The C₄ enzyme has a molecular weight of at least 250,000 (ref. 6) and can be assumed to be composed of more than one polypeptide chain. By preparing an enzyme of altered mobility and forming hybrids of it with the usual enzyme, we have obtained results that suggest that Cholinesterase is a tetramer.     

Production of θ Antibody by Mice that Fail to Reject θ-Incompatible Skin Grafts

EVIDENCE that female mice failing to reject male skin grafts are nevertheless producing H-Y antibody indicates that graft survival in this case is not due to failure of the recipient to respond to graft antigens¹. Survival of skin grafts in recipients that are producing specific anti-graft antibody is known in another system: radiation chimaeras of constitution (C57BL × A)→A often fail to reject C57BL skin grafts² although they are producing Sk alloantibody³. Sk alloantigens are limited to epidermal cells and brain and so give rise to skin-selective homograft reactions by radiation chimaeras^2,3.